This invention relates to apparatus for the horizontal continuous casting of metals, in particular steels.
Such apparatus customarily encompasses a container for the molten metal which has a discharge nozzle in the lower region of its wall through which the metal flows into a substantially horizontally arranged ingot mold out of which the metal strand is drawn off, generally by mechanical means. The molten metal is conducted out of the container into the mold through a discharge duct that may be, for example, in the form of a mouthpiece made of refractory material integral with the container and extending into the mold.
In the practice of continuous horizontal strand casting, it is sometimes necessary or desirable to interrupt the casting cycle rapidly, for instance, upon changing over to another product, to replace the mold while the container is filled with metal, or to perform repair work on the mold.
Thus, for instance, the French Pat. No. 1,181,408 discloses apparatus in which a container for the molten metal is connected via a vertical discharge opening with a horizontally arranged casting duct directly followed by a horizontal mold. The heatable casting duct situated beneath the discharge opening has an opening in the side away from the casting mold, and is designed to accommodate a horizontally displaceable closure plug that passes through said opening and that blocks or unblocks the vertical discharge opening of the molten metal container and the casting duct as desired in each given case. With the closure in the unblocked or opened state, the molten metal flows vertically out of the molten metal container and, by sharply changing direction, into the horizontally arranged casting duct and the subsequent continuous casting mold. If the flow of metal is to be interrupted, the closure plug, adapted to the internal shape of the casting duct, is pushed horizontally into the casting duct and closes the opening between the molten metal container and the casting duct, as well as the casting duct itself.
Such a simply designed horizontally working closure element has drawbacks in that, upon closing, a relatively large amount of metal is displaced and no means are provided for preventing clogging of the passage from the molten metal container to the casting duct, with the result that greater radiation and cooling of solidified metal remnants occur at that point, causing trouble in the operation of the closure element.
To alleviate these drawbacks in continuous casting plants with vertically arranged casting molds and horizontal slider plates arranged to close vertical discharge ducts, means have been developed to prevent solidification of the metal in the area of the shutoff element.
In the arrangement described in U.S. Pat. No. 3,809,146, the slider plate is designed as a divided unit and includes a porous segment corresponding substantially to the size of the discharge nozzle between the molten metal container and the mold. In the closed position of the slider plate, the porous segment is aligned with the discharge nozzle and coupled through a line to a gas supply. The gas is distributed through the porous segment and, by generating rising bubbles, maintains the molten metal permanently in movement, and prevents its penetration into readily cloggable areas and portions of the slider.
If the molten metal is hot and sufficiently fluid, an inert gas, such as, e.g., argon is introduced to achieve the desired displacement of the metal away from sensitive areas of the slider. If there is a risk of solidifying of the metal in the area of the discharge nozzle and the slider as a result of cooling, oxygen or oxygen-containing gas is substituted for the inert gas, whereby heating of the metal occurs in this area as a result of the oxidation of a small portion of the metal, thereby preventing solidification of parts of the metal in the area of the slider plate that is to retain its movability. Effective introduction of the gases is achieved without problems since, because of the horizontal disposition of the slider plate and the surface of the porous gas supply portion, the ferrostatic pressure of the metal situated above the slider in the container is uniform over the entire cross-section of the discharge nozzle.
However, in horizontal continuous casting plants where the closure means for interrupting the flow of molten metal from a horizontally disposed discharge nozzle comprises a vertically disposed sliding member, the ferrostatic pressure is not uniform over the entire cross-section of the discharge nozzle, there being a higher static pressure at the lower part of the sliding member than at its upper portion, giving rise to problems in avoiding unwanted solidification of the metal when the discharge nozzle is closed.